Method of providing arc-resistant dry type transformer enclosure

ABSTRACT

Arc resistant enclosures for dry-type transformers. More particularly, transformer enclosures having one or more arc-resistant features, including arc channels, arc fault dampers, and arc fault plenums, and methods for providing same.

FIELD OF INVENTION

The present application is directed to arc resistant enclosures fordry-type transformers, and more particularly, to a transformer enclosurehaving one or more arc-resistant features, including arc channels, arcfault dampers, and arc fault plenums. The present application is alsodirected to methods for providing an arc resistant enclosure fordry-type transformers.

BACKGROUND

Dry-type distribution and small power transformers are known in the art,and include a familiar core and winding configuration. It is common tohouse dry-type distribution transformers in metal enclosures for thepurposes of protecting the components from the environment and limitingexposure of people to the equipment, among others. Arc flash events canoccur in such electrical equipment during normal operation, systemtransients, or during maintenance. When an electric arc occurs withinthe enclosure, it results in a pronounced increase in the pressure andtemperature of gas within the enclosure. This sudden increase in gaspressure and temperature poses a risk of hot gas escaping the enclosurein an uncontrolled manner, which in turn poses a severe risk to peoplein the vicinity. It is therefore desirable to minimize such risk. Inparticular, it is desirable to prevent or minimize hot arc gasesescaping into the area surrounding the enclosure from the floor level toa height of 2 m (79 in.) from the floor level—ie., a standard measureapproximating the area within which personnel of average height wouldoccupy if such personnel were maintaining or operating the equipment.

SUMMARY

Described herein are multiple embodiments of an arc resistant enclosurefor dry-type transformer(s). In particular, in one embodiment, an arcresistant enclosure for housing dry type transformer(s) comprises baseand roof structures secured to at least three walls forming an enclosedspace. One of the walls is a front wall comprising a first and secondcorner piece, a first face frame proximate the first and second cornerpieces defining a first access opening, and a first access panelarranged to cover the first access opening. At least one ventilationopening is cut into the either the roof or walls. The front wallcontains at least one longitudinal seam covered by an arc channel,wherein the arc channel is attached in such a manner that, upon an arcevent, arc gas is substantially prevented from escaping the enclosurethrough the covered longitudinal seam. In at least one embodiment, anarc fault plenum is attached to the at least one ventilation opening.

In another embodiment, an arc resistant enclosure for dry-typetransformer(s) comprises base and roof structures secured to at leastthree walls, forming an enclosed space. At least one of the wallscontains at least one ventilation grating, and at least one ventilationopening is cut into either the roof or walls. An arc fault damperapparatus is affixed adjacent at least one of the ventilation gratings;providing, however, that an arc fault damper apparatus is affixedadjacent every ventilation grating that is located at or below a heightof 79 inches from the floor level. Finally, each arc fault damperapparatus is configured to close upon an arc flash event, therebysubstantially preventing the escape of arc flash gas through the atleast one ventilation gratings.

Methods for providing the aforementioned arc resistant enclosures areprovided herein.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, structural embodiments are illustratedthat, together with the detailed description provided below, describeexemplary embodiments of an arc resistant metal enclosures for dry-typetransformers, or components thereof. One of ordinary skill in the artwill appreciate that a component may be designed as multiple componentsor that multiple components may be designed as a single component.

Further, in the accompanying drawings and description that follow, likeparts are indicated throughout the drawings and written description withthe same reference numerals, respectively. The figures are not drawn toscale and the proportions of certain parts have been exaggerated forconvenience of illustration.

FIG. 1A is an isometric view of a prior art transformer enclosurehousing a three-phase dry-type distribution transformer, with a sidewallremoved.

FIG. 1B is an isometric view of an exemplary arc resistant dry-typetransformer enclosure, with the arc plenums removed.

FIG. 1C is an exploded partial view of the enclosure of FIG. 1B, showingthe base structure, front wall, and first sidewall.

FIG. 2A is an isometric view of the inside surface of an exemplary arcchannel, without end-cap pieces.

FIG. 2B is an elevational view along the longitudinal axis of the arcchannel of FIG. 2A, with an end-cap piece.

FIG. 3A is an isometric, exploded, and enlarged view of the portionshown in the dashed line 2 of FIG. 1B.

FIG. 3B is a sectional view of enclosure 100 along line 3-3′ in FIG. 1B.

FIG. 3C is a sectional view of enclosure 100 along line 4-4′ in FIG. 1B.

FIG. 3D is a sectional view of enclosure 100 along line 5-5′ in FIG. 1B.

FIG. 3E is a sectional view of enclosure 100 along line 6-6′ in FIG. 1B.

FIG. 3F is a sectional view of enclosure 100 along line 7-7′ in FIG. 1B.

FIGS. 4A and 4B are isometric exploded views of an exemplary arc faultdamper apparatus from the front and rear, respectively.

FIG. 5A is an isometric, enlarged view of the portion shown in thedashed line 8 of FIG. 1B.

FIG. 5B is an isometric view from the rear of an exemplary arc damperapparatus in a closed configuration.

FIG. 6A is an isometric, enlarged view of the portion shown in thedashed line 8 of FIG. 1B.

FIG. 6B is an isometric view from the rear of an exemplary arc damperapparatus in an open configuration.

FIG. 7A is an isometric view of an exemplary arc fault plenum, viewedfrom above and from the rear.

FIG. 7B is an isometric view of the arc fault plenum shown in FIG. 7A,viewed from below and from the rear.

FIG. 7C is an isometric view of a flanged square piece used to build thearc fault plenum segment in FIG. 7D.

FIG. 7D is an isometric view of an arc fault plenum segment used tobuild the arc fault plenum in FIG. 7A.

FIGS. 8A and 8B are front and rear isometric views of the exemplary arcresistant dry-type transformer enclosure of FIG. 1B, including the arcfault plenum in FIG. 7A, as attached.

DETAILED DESCRIPTION

The enclosures and principles disclosed in this application areapplicable to dry-type transformers of various sizes and ratings.Non-limiting examples of suitable dry-type transformers for use hereininclude power or distribution dry transformers with power ratings from112.5 kVA to 25 MVA. Non-limiting examples of suitable commerciallyavailable dry transformers include vacuum cast coil, RESIBLOC® and openwound transformers offered by ABB, Inc.

FIG. 1A shows a typical three-phase dry-type distribution transformer 10housed in enclosure 20. For ease of reference, dry-type transformerswill be referenced hereinafter simply as transformers.

With reference to FIGS. 1B and 1C, a transformer enclosure 100 accordingto one embodiment of the present invention is shown. Enclosure 100includes a base structure 110, walls 120, and a roof structure 150. Thebase structure may include means for supporting a transformer (notshown) within the enclosure, such as brackets 115. The walls 120 aresecured to the base structure 110, typically at the bottom portion ofthe walls 120. Walls 120 are preferably substantially perpendicular tothe base structure 110, e.g., at an angle of approximately 90°, such asbetween 80°-100°. As will be appreciated, in other embodiments, walls120 and base structure 110 may form an angle substantially differentfrom 90°, such as 30°, 45°, 60°, 120°, 135°, 150°, and any of variousangles therebetween. Walls 120 are preferably secured around theperimeter of the base structure 110. Alternatively, walls 120 aresecured at any point of the base structure 110.

Although a rectangular enclosure is depicted in FIGS. 1B and 1C, it willbe understood that the enclosure walls 120 may form any of a number ofgeometric shapes, such polygonal, i.e., triangle, square, pentagon,etc., or can be circular, oval, elliptical, and the like. Moreover, anynumber of walls 120 may be employed.

Roof structure 150 is secured to the top of walls 120 and may compriseone or more generally flat, rigid panels. Roof structure 150 may containone or more ventilation openings, or holes, 155 that permit ventilationof the interior of the enclosure. In one embodiment, roof structure 150comprises three flanged and interlocked roof panels 150 a-c, with eachroof panel containing a ventilation opening 155 a-c in the centerthereof. As will be appreciated, although a flat, multi-paneled roofstructure 150 is depicted in FIGS. 1B and 1C, in other embodiments, roofstructure 150 may be comprised of any suitable number of panels havingany suitable geometric shape. For example, in one embodiment, roofstructure 150 comprises a single flat, rigid panel containing a singleventilation opening. The roof structure and ventilation openings aredescribed in more detail below, in the context of arc plenums.

Enclosure 100 is fabricated using generally any material that is capableof providing the functional requirements of the user, including arcfault resistance. In one embodiment, enclosure 100 is fabricated usingheavy gauge sheet steel; in other embodiments, enclosure 100 isfabricated using heavy gauge aluminum or stainless steel. The enclosure100 may comply with National Electrical Manufacturers Association (NEMA)250 Standards.

With reference again to FIGS. 1B and 1C, in the embodiment shown,rectangular enclosure 100 has a front wall 120 a, a first sidewall 120b, a back wall 120 c (not shown), and a second sidewall 120 d (notshown). In this embodiment, the front and back walls are similarlyconfigured, and the first and second sidewalls are similarly configured.As such, only front wall 120 a and first sidewall 120 b are referencedhereinafter. As may be appreciated, in other embodiments, the walls maybe differently configured.

In the embodiment shown, front wall 120 a is comprised of a rigid faceframe 125 that is itself comprised of two identical face frames 126 and127 arranged in a coplanar and adjacent manner. Face frame 126 has firstand second longitudinal edges bearing first and second longitudinalflanges 128, 129 that extend inwardly from and perpendicularly to theplane of face plate 126. Likewise, second face frame 127 has first andsecond longitudinal edges bearing first and second longitudinal flanges130, 131 that extend inwardly from and perpendicularly to the plane offace frame 127. Longitudinal flanges 129, 130 are mechanically affixed,via bolts or otherwise, forming fourth longitudinal seam 170 d, therebyproviding rigid face frame 125. As will be appreciated, rigid face frame125 may also be comprised of a single face frame, thereby eliminatingthe need for longitudinal flanges 129, 130.

First and second face frames 126, 127 each contain first and secondaccess openings 132 a,b that define a majority of the surface area ofthe face frames and provide access to the interior of enclosure 100.Access opening 132 a is defined on its longitudinal sides by a pair ofgenerally U-shaped channels 133 a,b, that extend along the length of theaccess opening; likewise, access opening 132 b is defined on itslongitudinal sides by a pair of generally U-shaped channels 133 c,d,that extend along the length of that access opening. The structure andfunction of channels 133 are detailed, below, in relation to FIG. 3A.

With continued reference to FIGS. 1B and 1C, the front wall 120 a iscomprised of first and second corner pieces 134, 136. Corner pieces 134,136 are rigid, unitary panels that are curved or angled in a manner toform a first portion 134 a, 136 a, and a second portion 134 b, 136 b.The angle defined by first and second portions depends on the geometricshape of enclosure 100. In the embodiment shown, the angle is 90°. Firstportion 134 a, 136 a is generally co-planar with face plate 125 andforms part of front wall 120 a, while second portion 134 b, 136 b formspart of sidewalls 120 b, d and are co-planar with the remainingcomponents of those wall, described below.

Corner piece 134 is adjacent first face frame 126, and the longitudinaledge of corner piece 134 that is proximate face plate 126 bears a flange135 that is directed inwardly and perpendicularly to the plane of frontwall 120 a, Likewise, corner piece 136 is adjacent second face frame127, and the longitudinal edge of corner piece 136 that is proximateface frame 127 bears a flange 137 that is directed inwardly andperpendicularly to the plane of front wall 120 a, As assembled, flange135 is mechanically affixed, by bolting or otherwise, to first flange128 of face frame 126, forming first longitudinal seam 170 a, Likewise,as assembled, flange 137 of corner piece 136 is mechanically affixed tosecond flange 131 of face frame 127, forming seventh longitudinal seam170 g.

Front wall 120 a may also comprise one or more rigid access panels 140.In the embodiment shown, front wall 120 a comprises first and secondrigid access panels 140 a, b that are configured and arranged to coveraccess openings 132 of face frame 125. Access panels 140 aremechanically affixed to face frame 125 by any suitable means. In oneembodiment, access panels 140 are configured such that each longitudinalside is flanged in a manner to mate with U-shaped channels 133 of faceframe 126, 127, and are bolted along their length to face frame 125 inthe manner described below.

Front wall 120 a may also comprise one or more ventilation gratings 180that allow gas to pass into and out of the interior of the enclosure. Inthe embodiment shown, access panels 140 each contain two ventilationgratings 180. In other non-limiting embodiments, the one or moreventilation gratings are located in one or more different locations,such as sidewalls 120 b,d, and/or back wall 120 c.

Sidewall 120 b comprises one or more rigid sidewall plates 145. In theembodiment shown, sidewall 120 b comprises two identical sidewall platesseparated by, and affixed to, an elongated sidewall support piece 146.Additionally, sidewall 120 b comprises second portion 136 b of cornerpiece 136, as well as an analogous second portion of counterpart cornerpiece 138.

Arc Channels

With continued reference to FIGS. 1B and 1C, arc channels 160 accordingto one embodiment of the present invention are shown. In general, arcchannels 160 are elongated flat metal pieces having first and secondends 161, 162 that are positioned on the enclosure at a first pointproximate the floor and a second point greater than 2 m (79 in.) abovethe floor level, respectively. Arc channels 160 are affixed to the outersurface of walls 120 at any longitudinal seam or portion of anylongitudinal seam, as that term is defined herein, that is locatedanywhere from the floor level to 2 m (79 in.) from the floor level. Theterms “seam” and “joint” are used interchangeably herein and refer toany longitudinal seam in the outer surface of walls 120 caused by theabutment or overlap of two adjacent wall panels, frames, or supportpieces, that are likely to release expanding gas resulting from an arcfault event, and that are thereby likely to cause harm directly to anyadjacent bystander or indirectly by igniting adjacent flammablematerial.

Arc channels 160 act to contain rapidly expanding gases resulting froman arc fault event inside the enclosure, or to direct expanding gases toa point that will not be likely to cause harm (e.g., to a point higherthan 79 in. above floor level). Referring to FIGS. 2A and 2B, in oneembodiment, arc channels 160 have a central flat elongated portion 163and two side portions 164. Side portions 164 are formed by angling eachside twice at approximately 90°, creating a turned-up portion 164 a anda flanged portion 164 b that is approximately parallel to the centralportion 163. Preferably, both ends 161 and 162 of arc channel 160 aresubstantially closed or capped by, for example, welding a small flatmetal end-cap piece 165 to either end such that the cross-sectional areabetween each turned-up portion 164 a is substantially covered, as shownin FIG. 2B. Each arc channel 160 is attached to the outer surface of theenclosure walls 120 such that the flanged portions 164 b abut the outersurface, thereby creating an enclosed space (not shown) between theouter surface of the enclosure walls 120 and the inner surface of theflat elongated portion 163.

FIG. 3A is an exploded and enlarged view of the portion shown in thedashed line 2 in FIG. 1B, showing an upper section of arc channel 160 b,a portion of access panel 140 a, and a portion of face frames 126, 127that are mechanically affixed by longitudinal flanges 129, 130 and thatcontain U-shaped channels 133 b and 133 c, respectively. As assembled,access panel 140 a is brought into contact with face frame 126 such thatits first longitudinal side, which is flanged perpendicularly to itssurface, is seated in first U-shaped channel 133 a (not shown) of faceframe 126 and its second longitudinal side, which is also flangedperpendicularly to its surface, is seated in second U-shaped channel 133b. Likewise, although not shown in FIG. 3A, access panel 140 b isbrought into contact with face frame 127 such that its firstlongitudinal side, which is flanged perpendicularly to its surface, isseated in first U-shaped channel 133 c of face frame 127 and its secondlongitudinal side, which is flanged perpendicularly to its surface, isseated in second U-shaped channel 133 d.

With continued reference to FIG. 3A, one exemplary arc channel boltingarrangement is shown. In this embodiment, both the arc channel 160 b andaccess panel 140 a are bolted to face frame 126 using two alternatingsets of bolts. A first set of bolts 300 passes through arc channel 160 balong a line proximate one longitudinal edge of arc channel 160 b.Thereafter, the bolts 300 pass through access panel 140 a and screw intoa securing means, e.g., a tinnerman nut (not shown), in face frame 126.A second set of bolts 310 originate inside arc channel 160 b (i.e., thehead of bolts 310 lie within the enclosed space between flat elongatedportion 163 of arc channel 160 and the access panel 140), pass throughaccess panel 140 a, and screw into a securing means, e.g., a tinnermannut (not shown), in face frame 126. Likewise, this bolting arrangementis utilized along a line proximate the opposite longitudinal edge of arcchannel 160 b to affix arc channel 160 b and access panel 140 b to faceframe 127. In this manner, arc channel 160 b covers the third, fourth,and fifth longitudinal seams 170 c,d,e, described n more detail below.

FIG. 3B is a sectional view of enclosure 100 along line 3-3′ in FIG. 1B,showing an assembled cross-section of a portion of front wall 120 a, andspecifically portions of corner piece 134 a, arc channel 160 a, faceframe 126, and access panel 140 a, As shown, first longitudinal seam 170a is formed by the abutting flange portions 135, 128 of corner piece 134and face frame 126, respectively. Also, second longitudinal seam 170 bis formed by the overlapping portion of access panel 140 a and faceframe 126. A first set of bolts 320 is proximate a first longitudinaledge of arc channel 160 a, bolting it to corner piece 134; second andthird alternating sets of bolts 300, 310, bolts a second longitudinaledge of arc channel 160 b to access panel 140 a and face frame 126. Inthis manner, arc channel 160 a covers first and second seams 170 a,b.

FIG. 3C is a sectional view of enclosure 100 along line 4-4′ in FIG. 1B,showing an assembled cross-section of a portion of front wall 120 a, andspecifically portions of arc channel 160 b, access panels 140, and faceframes 126, 127. As shown, third and fifth longitudinal seams 170 c,eare formed by overlapping portions of access panel 140 and face frames126, 127, respectively, as described above. Similarly, fourthlongitudinal seam 170 c is formed by the abutting flange portions 129,130 of face frames 126 and 127, respectively, as described above. Alsoas shown, arc channel 160 b is bolted to access panel 140 a and faceframe 126, and access panel 140 b and face frame 127, using bolts 300,310, as described above, thereby covering third, fourth, and fifthlongitudinal seams 170 c,d,e.

FIG. 3D is a sectional view of enclosure 100 along line 5-5′ in FIG. 1B,showing an assembled cross section of a portion of front wall 120 a andsidewall 120 b, and specifically portions of access panel 140 b, faceframe 127, arc channel 160 c, corner piece 136, arc channel 160 d, andsidewall panel 145 a. As shown, sixth seam 170 f is formed by theoverlapping portion of access panel 140 b and face frame 127. Seventhseam 170 g is formed by the abutting flange portions 131, 137 of faceframe 127 and corner piece 136 a, respectively. First and secondalternating sets of bolts 300, 310 are proximate a first longitudinaledge of arc channel 160 c, bolting it to access panel 140 b and faceframe 127, in the manner described above. Also, a third set of bolts 320is proximate a second longitudinal edge of arc channel 160 c, bolting itto corner piece 136 a. In this manner, arc channel 160 c covers sixthand seventh seams 170 f,g.

With continued reference to FIG. 3D, eighth longitudinal seam 170 h isformed by the overlapping portion of sidewall panel 145 a and cornerpiece 136 b. A first set of bolts 330 is proximate a first longitudinaledge of arc channel 160 d, bolting it to corner piece 136 b. Second andthird alternating sets of bolts 340, 350 are proximate a secondlongitudinal edge of arc channel 160 d, bolting it to sidewall panel 145a and to corner piece 136 b. In this manner, arc channel 160 d coverseighth seam 170 h.

FIG. 3E is a sectional view of enclosure 100 along line 6-6′ in FIG. 1B,showing an assembled cross section of a portion of sidewall 120 b, andspecifically portions of sidewall panels 145 a,b, sidewall support piece146, and arc channel 160 e. As shown, ninth and tenth seams 170 i,j, areformed by the overlapping portions of sidewall panels 145 a,b, andsidewall support piece 146, respectively. First and second alternatingsets of bolts 340, 350 are proximate to both longitudinal edges of arcchannel 160 e, bolting it to sidewall panels 145 and to sidewall supportpiece 146. In this manner, arc channel 160 e covers ninth and tenthseams 170 i,j.

FIG. 3F is a sectional view of enclosure 100 along line 7-7′ in FIG. 1B,showing an assembled cross section of a portion of sidewall 120 b, andspecifically portions of sidewall panel 145 b, arc channel 160 f, andcorner piece 138. As shown, eleventh seam 170 k is formed by theoverlapping portion of sidewall panel 145 b and corner piece 138. Firstand second alternating sets of bolts 340, 350 are proximate a firstlongitudinal edge of arc channel 160 f, bolting it to sidewall panel 145b and to corner piece 138. A third set of bolts 330 is proximate asecond longitudinal edge of arc channel 160 f, bolting it to cornerpiece 138. In this manner, arc channel 160 f covers eleventh seam 170 k.

Arc channels 160 a-f, described above, cover longitudinal seams 170 a-k,thereby preventing or minimizing the escape of hot gas resulting from anarc flash event in the area surrounding enclosure 100 below a height of2 m (79 in.). In this way, any personnel in the vicinity are protectedfrom exposure to such hot gases, as well as any flammable materials. Asmay be appreciated, the arc channels described herein are merely oneembodiment of the present invention, and different configurations,geometries, and attachment means for other arc channel embodiments arecontemplated herein that may still perform the functions describe above.Likewise, different seam geometries and arrangements may be present indifferent enclosure embodiments, depending on the particular enclosureembodiment.

Arc Fault Damper Apparatus

Embodiments of the present invention may also include one or more arcfault damper apparatus. In general, an arc fault damper apparatus is adamper device that is located and coupled with ventilation gratingsdescribed above. According to the invention described herein, anyventilation grating that is present in an arc resistant transformerenclosure at a location that is at or below a height of 2 m (79 in.)from the floor level must have an arc fault damper apparatus coupledtherewith.

With reference to FIGS. 4A and 4B, an arc fault damper apparatus 400according to one embodiment of the present invention is shown. Damperapparatus 400 includes a damper plate 405 that is made from any materialsuitable to prevent hot arc gases from escaping an enclosure and that isshaped so as to completely cover the ventilation grating that it isassociated with. In one embodiment, damper plate 405 is made of steeland is rectangular, with an area greater than the area covered byventilation grating 180. A damper handle 410 is attached to the frontsurface (shown in FIG. 4A) of damper plate 405 and is arranged toprotrude through a suitable opening in ventilation grating 180.

In one embodiment, the top edge of damper plate 405 bears a flange 415that extends in a direction toward the rear surface (shown in FIG. 4B)of damper plate 405, and that is perpendicular to the surface plane.Also, both side edges of damper plate 405 bear first and second sideflanges 420 a,b that extend in a direction toward the rear surface ofdamper plate 405 and that are perpendicular to the surface plane. Sideflanges 420 each include throughhole 441 and bolt channel 451, describedin more detail below.

One or more hinges are attached to the damper plate in order torotatably attach the damper plate to the inside surface of enclosure100. In one embodiment, elongated hinge 425 is attached to top flange415.

Arc fault damper apparatus 400 includes one or more brackets. In oneembodiment, first and second brackets 430 a, b include a flanged portionthat is substantially co-planar with the surface of damper plate 405 anda main portion that extends rearwardly from the flanged portion and thatis substantially perpendicular to the flanged portion. The main portioncomprises at least one wheel bearing channel 431 having a notch 432, andat least one cutout portion 433, all of which are described in moredetail below.

With continued reference to FIGS. 4A and 4B, the upper portion ofbracket 430 is rotatably attached to damper plate 405 by bolt 435 in thefollowing manner. Bolt 435 extends through angled outer spring retainer440, cutout portion 433, throughhole 441, and thereafter through innerspring retainer 442, and is secured by locking washer 491 and nut 436,which is threadably attached. Flat washers 490 are included atappropriate positions, as shown. Cutout portion 433 is configured toprovide a suitable throughhole for bolt 435 at the top portion ofbracket 430. In the embodiment shown, cutout portion 433 includes arelatively larger upper portion to accommodate bolt 435, a relativelynarrow necking portion that has a width less than the diameter of bolt435 (thereby preventing bolt 435 from moving past it), and a relativelylarge lower portion that serves to reduce the weight of the bracket 430and to allow increased ventilation when damper plate 405 is open.

The lower portion of bracket 430 is slidably attached to damper plate405 by bolt 445 in the following manner. Bolt 445 extends through angledouter spring retainer 450, bearing wheel 455, bearing channel 431, boltchannel 451, and thereafter through inner spring retainer 452, and issecured by locking washer 492 and nut 446, which is threadably attached.Flat washers 490 are included at appropriate positions, as shown.

Outer springs 460 are attached at a first end to outer spring retainer440, and at a second end to outer spring retainer 450. Similarly, innersprings 465 are attached at a first end to inner spring retainer 442 andat a second end to inner spring retainer 452. Bearing wheels 455 aresituated in bearing channel 431.

The operation of arc fault damper apparatus 400 is described withadditional reference to FIGS. 5A, 5B, 6A and 6B. FIG. 5B is a rear viewof arc fault damper apparatus 400, as assembled and in a closedposition. Damper apparatus 400 is aligned with a ventilation grating180, described above and shown in FIG. 5A. Side brackets 430 and hinge425 are attached to access panel 140 a of enclosure 100, as by boltingor the like, such that damper 405 completely covers grating 180. Anexemplary bolting pattern is shown in FIGS. 5A and 5B, and comprises thealigned bolt holes 500 a, b of side brackets 430 a, b with bolt holes505 a,b of access panel 140 a, and the aligned bolt holes 500 c of hinge425 with bolt holes 505 c of access panel 140 a.

Arc fault damper apparatus 400 is configured such that it is in anormally closed position, as shown in FIGS. 5A and 5B. In the embodimentshown, the normally closed configuration is accomplished through the useof outer and inner springs 460, 465, combined with bearing wheels 455and an angled bearing channel 431. In particular, a first end of outerand inner springs 460, 465 is attached to outer and inner springretainers 440, 442, respectively, which in turn are rotatably affixed inposition by bolts 435. A second end of springs 460, 465 is attached toouter and inner spring retainers 450, 452, respectively, which in turnare rotatably mounted on bearing wheels 455. Bearing wheels 455, whichare mounted in angled bearing channel 431, allow springs 460, 465 totransfer a contraction force into a lateral force that effectively pullsdamper 405 to a closed position. As may be appreciated, otherarrangements may be configured to result in a normally closed damper405, and are encompassed herein. In one non-limiting example, bearingwheels 455 are replaced by steel pins that are capable of sliding inbearing channels 431. In another non-limiting example, torsion springsare utilized at bolts 435 in lieu of the components discussed above.

In normal operation, an operator sets damper 405 to an open position (asshown in FIGS. 6A and 6B) by pushing damper handle 410 until bearingwheel 455 is seated in notch 432. Once seated, damper 405 will remainopen and thereby allow ventilation of enclosure 100 to occur. Upon anarc event, however, the concussive force of a the rapidly expandinggases unseats bearing wheel 455, causing the damper 405 to move to aclosed position, thereby preventing substantial escape of the heated arcgases from enclosure 100 through the ventilation gratings 180.

Arc Fault Plenum

Embodiments of the present invention may also include one or more arcfault plenums. In general, an arc fault plenum is an enclosure apparatusthat channels expanding arc fault gases out of the arc resistanttransformer enclosure to a location where they may be safely discharged.

Referring to FIGS. 7A-7D, arc fault plenums 700 according to oneembodiment of the present invention are shown. In general, arc faultplenum 700 may be constructed of any material suitable for containingarc fault gases. In one non-limiting embodiment, arc fault plenum isconstructed of light gauge sheet metal.

Arc fault plenum 700 may be constructed in segments 710, of any suitableshape or length, that are mechanically attached as by bolting or thelike. In one non-limiting embodiment, each segment 710 is cubic andcomprised of identical square pieces 720 that are flanged at each sidein a direction perpendicular to its surface. Each segment 710 is formedby attaching a first flange of side square pieces 730 to a first surface(ie., the surface that does not intersect a flange) of top square piece740 proximate two of its opposing edges. Similarly, a second flange(ie., opposite the first flange) of side square pieces 730 are attachedto the first surface of bottom square piece 750 proximate two of itsopposing edges. Each segment 710 is thereafter attached via flanges toanother segment 710 to arrive at arc fault plenum 700, with the provisothat a bottom square piece 750 is not attached to one or moreconsecutive segments 710, so as to provide an open space 760.

Referring to FIGS. 8A and 8B, arc resistant enclosure 100 is shownhaving arc fault plenum 700 attached. In the embodiment shown, arc faultplenum 700 is bolted to roof structure 150 such that open spaces 760 arealigned with ventilation opening 155, shown in FIGS. 1B and 1C, and suchthat expanding arc fault gases may exit the interior of enclosure 100via ventilation opening 155 and arc fault plenum 700. In onenon-limiting embodiment, arc fault plenum 700 is connected to a ductsystem that terminates in a safe location outside of the electrical roomand/or building housing enclosure 100.

As may be appreciated, other arc fault plenum and ventilation openingconfigurations are within the scope of the present invention. Forexample in one non-limiting embodiment, roof structure 150 comprises asingle panel with a single ventilation opening, to which a single arcfault plenum is attached. In other non-limiting embodiments, ventilationopenings 155 are provided in one or more enclosure wall 120, at a pointabove 2 m (79 in.) from the floor, and one or more arc fault plenums areattached thereto.

To the extent that the term “includes” or “including” is used in thespecification or the claims, it is intended to be inclusive in a mannersimilar to the term “comprising” as that term is interpreted whenemployed as a transitional word in a claim. Furthermore, to the extentthat the term “or” is employed (e.g., A or B) it is intended to mean “Aor B or both.” When the applicants intend to indicate “only A or B butnot both” then the term “only A or B but not both” will be employed.Thus, use of the term “or” herein is the inclusive, and not theexclusive use. See, Bryan A. Garner, A Dictionary of Modern Legal Usage624 (2d. Ed. 1995). Also, to the extent that the terms “in” or “into”are used in the specification or the claims, it is intended toadditionally mean “on” or “onto.” Furthermore, to the extent the term“connect” is used in the specification or claims, it is intended to meannot only “directly connected to,” but also “indirectly connected to”such as connected through another component or components.

While the present application illustrates various embodiments, and whilethese embodiments have been described in some detail, it is not theintention of the applicant to restrict or in any way limit the scope ofthe appended claims to such detail. Additional advantages andmodifications will readily appear to those skilled in the art.Therefore, the invention, in its broader aspects, is not limited to thespecific details, the representative embodiments, and illustrativeexamples shown and described. Accordingly, departures may be made fromsuch details without departing from the spirit or scope of theapplicant's general inventive concept.

1. A method of providing an arc resistant enclosure for a dry typetransformer, comprising the steps of: providing a base structure;providing a dry-type transformer seated on the base structure; providingat least three walls secured to the base structure, forming an enclosedspace for housing the transformer, at least one of the walls containingat least one ventilation grating; providing a roof structure secured tothe walls; providing at least one ventilation opening in either the roofor walls; wherein an arc fault damper apparatus is affixed adjacent atleast one of the at least one ventilation gratings, with the provisothat an arc fault damper apparatus is affixed adjacent every ventilationgrating that is located at or below a height of 79 inches from the floorlevel, and wherein each arc fault damper apparatus is configured toclose upon an arc flash event, thereby substantially preventing theescape of arc flash gas through the at least one ventilation gratings.2. The method of claim 1, wherein the at least three walls comprise afront wall, two sidewalls, and a back wall, wherein the front wallcomprises a first and second corner piece, a first face frame defining afirst access opening and a second face frame defining a second accessopening, wherein the first face frame is proximate the first cornerpiece and the second face frame is proximate the first face frame andthe second corner piece, wherein a first access panel covers the firstaccess opening and a second access panel covers the second accessopening, and wherein the first and second access panels each contain atleast one ventilation grating having an arc fault damper apparatusaffixed adjacent thereto.
 3. The method of claim 1, further comprisingthe step of providing an arc fault plenum connected to the at least oneventilation opening.
 4. The method of claim 2, further comprising thestep of providing an arc fault plenum connected to the at least oneventilation opening.
 5. The method of claim 3, wherein the at least oneventilation opening is located on the roof structure.
 6. The method ofclaim 4, wherein the at least one ventilation opening is located on theroof structure.
 7. The method of claim 5, wherein the roof structurecontains three ventilation openings and an arc fault plenum is attachedto each ventilation opening.
 8. The method of claim 6, wherein the roofstructure contains three ventilation openings and an arc fault plenum isattached to each ventilation opening.
 9. The method of claim 7, whereineach arc fault plenum comprises at least three flanged segments.
 10. Themethod of claim 8, wherein each arc fault plenum comprises at leastthree flanged segments.